Courts have interpreted the act of sex as being a contract to have children. How is what this cut & run lesbian did any different? It appears the court acknowledges they had an agreement, it's just that they refuse to enforce it.
She's different in that the child isn't biologically hers. OTOH, the sperm donor knowingly and deliberately did his part to conceive the child. How can you not see the difference?
Of course, I wouldn't object to making her pay child support, except that then you would have a legal case for making men who aren't the biological fathers pay child support, and there's too much of that already.